1. Field of the Invention
The invention relates to a display device having a microcontroller, a graphics controller, and a pointer driven by means of a stepper motor. The graphics controller does not have an arithmetic logic unit and can be controlled by the microcontroller and by command sequences of a command sequencer contained in the graphics controller. In this arrangement, the graphics controller contains one or more stepper motor controllers and the command sequencer contains a watchdog timer.
2. Description of the Related Art
Special graphics controllers are used especially in displays in motor vehicles for reducing the workload of the microcontrollers and, nevertheless, being able to control complex, displays. In this context, the microcontroller controls the graphics controller that drive one or more electrooptical displays and one or more pointer instruments driven via a stepper motor. Such a graphics controller is known, for example, as the graphics controller MB88F332 by the company Fujitsu.
When the microcontroller and the graphics controller, due to a special construction of the display device, are not arranged on a common circuit board but on different circuit boards, the physical and logical connection of the microcontroller and the graphics controller is monitored. In the case of a fault, a user of the display device is provided with a clear indication that the display device exhibits a fault. In the case of a combined instrument of a motor vehicle, for example, this is intended to occur due to the fact that the pointers of an existing tachometer and a speedometer are moved into a home position, for example a zero position, so that a corresponding user of the display device is clearly presented with the fault case. The aforementioned graphics controller does not contain an arithmetic logic unit to move the existing pointer instrument into a home position in the case of a fault.